A die-cast material which is one of aluminum cast materials and a wrought material such as an aluminum extruded material are both widely used in the fields of automobiles, ships, industrial machines and the like. That is because various thin, complicatedly-shaped and high-precision parts can be made of the die-cast material, and the wrought material has excellent strength characteristics.
In these years, there has been a growing demand for automotive lightening against the background of an increasingly-required environmental quality improvement. As one means for meeting the demand, welded structures each obtained by weld-connecting the above-mentioned die-cast material and wrought material together by arc welding have been increasingly employed as structures constituting vehicle bodies, suspensions and the like.
In addition, to employ these welded structures, it is essential that the reliability of welding quality should be secured, and particularly the welding strength should be secured, because these welded structures need to bear external forces produced while the automobile is running. Specifically, it is essential that, when a welded structure breaks, the breakage should occur only in the die-cast materials or wrought materials.
However, when an aluminum die-cast material and an aluminum wrought material are arc-welded together, the welding strength decreases in the weld zone because a gas contained in the die-cast material creates blowholes in the weld zone.
With this taken into consideration, for example, as disclosed in Japanese Patent Application Publication No. Hei. 8(1996)-206838, when a DC pulsed arc welding is carried out, the blowholes are reduced by agitating the molten weld pool by use of an agitator, heating the molten weld pool by use of a heater, and the like.
Moreover, as disclosed in Japanese Patent Application Publication No. Hei. 10(1998)-314948, a part of an aluminum die-cast member in a vicinity of a boundary between the aluminum die-cast member and an aluminum material to be connected to the aluminum die-cast member is fused by an alternating current TIG arc welding method, and thereby a gas contained in the part of the aluminum die-cast member in the vicinity is released from the part. Once the part of the aluminum die-cast member in this vicinity is solidified, the aluminum die-cast member and the aluminum material to be connected to the aluminum die-cast member are welded by an alternating current TIG filler arc welding method.
In addition, Japanese Patent Application Publication No. 2005-34868 discloses a combination of laser radiation and an arc length oscillation pulse arc welding method. The arc length oscillation pulse arc welding is carried out while irradiating a laser beam to the vicinity of a front boundary between a melted zone and an unmelted zone in a molten pool, so that gas is released from the melted zone with the laser irradiation during the welding.